This invention relates generally to methods and apparatus for computed tomography (CT), and more particularly to methods and apparatus that provide for a field replaceable CT digital module.
Modular radiation detector arrays typically include a collimator, a scintillator array or package, and a photo diode assembly. The collimator, scintillator package “pack”, and diode assembly are precision aligned and attached together to form a detector module. A number of modules are mounted on rails to form the detector array, and pins are fabricated in the pack to enable precise positioning of the pack onto the rails.
The accurate positioning of the collimator, scintillator package, and diode assembly to attach and optically couple them together can be problematic. Additionally, the accurate positioning of the modules relative to one another to form the detector array can be problematic. Because of the X-ray to light conversion process, it is useful that the analog area of a CT module be sealed against all light sources. Further, in order to allow installation and removal of the digital module, a card guide is required to properly align the module for installation and extraction for a CT system. Moreover, the analog portion of the module is subject to Electromagnetic interference (EMI) and requires EMI protection.
One problem with installing a digital module is that the analog module with a pin-in-pack alignment feature is typically moved in the detector Z direction, such that the analog module does not make contact with the collimator rails, before aligning the pin in pack. The digital module is then typically moved in the detector Y direction to bring the analog module into position so that the pin in pack feature engages the collimator combs without damaging a collimator plate. This complex motion has traditionally precluded replacement of modules in the field. The current practice is to use non-field serviceable analog detector modules that, on occasion, experience a failure in the field. When such failure occurs, the entire detector is removed from the CT system, returned to the factory for disassembly and repair. This current practice is costly and time-consuming.